The invention relates to a device for checking a loading state, i.e. a piece of electronic equipment which at any instant determines the weight of a mass suspended from the hook of a lifting appliance and compares it with a load diagram corresponding to the optimum possibilities of the machine.
This device for checking a loading state is especially designed to equip telescopic cranes, but its use may be extended to all types of lifting appliance such as lattice cranes and tower cranes whereof the parameters taken into account in these two examples are much less numerous.
Generally, it is known that telescopic cranes are so-called quick-action lifting appliances and are generally self-propelled and self-contained. However, if the fact that they are able to travel on the road fairly quickly has a certain advantage, this also imposes strict rules for their use, since they are lifting appliances which operate with an overhang.
The lifting capacity of a telescopic crane is limited by the stability in certain operating positions and by mechanical strength in other positions.
The maximum load which a crane is able to lift thus depends on numerous parameters such as: the reach, the length of the jib, the angle of the jib, the adjustment, the orientation of the turret etc.
All these parameters are involved according to very complex laws, such that the manufacturers of lifting appliances are compelled to provide load diagrams which are peculiar to each type of crane.
These load diagrams define the range of use of the crane very well, but are not always respected by the user who always encounters enormous difficulties in permanently evaluating certain factors, such as the load, the reach or even the angle of the jib.
The invention therefore relates to a device for checking a loading state, whose essential purpose is to collect all possible information relating to the appliance, to process this information in order to obtain the parameters used in the diagrams and to compare these parameters with the load diagrams provided by the manufacturer.
Finally, this equipment provides the crane driver with essential information for driving the crane, namely the loading state which, for a given operating position, is the ratio of the actual load suspended from the hook to the maximum admissible load.
Normally, this single piece of information is sufficient to enable the crane driver to work without exceeding the limits of his crane, but other pieces of information, such as the reach and angle of the jib could be given to the driver as an indication.
According to the invention, in order to provide a signal representative of the loading state of the crane, the checking device firstly comprises a memory section in which all the information contained in the diagrams provided by the manufacturer is stored, these diagrams providing the values of maximum admissible load depending on the various values of two parameters defining the geometric state of the crane, a central unit which firstly receives the actual values of the various parameters of the crane and secondly the value of the load on the crane hook.
By means of memorized values, this central unit determines the maximum admissible load and essentially compares this load with the actual load on the crane hook. It is also able to provide the ratio of actual load/maximum admissible load which as afore-mentioned is the loading state of the crane.
It is obvious that the determination of the maximum admissible load depending on the stored values depends on the nature of the diagrams provided by the manufacturer and on the capacity of the memories used in the device for checking the loading state.
When the capacity of the memories is considerable and sufficiently accurate diagrams are available, the function of the central unit is reduced to simple addressing which, for each of the values of the pair of parameters, makes it possible to obtain the value of the maximum admissible load for this pair of parameters.
When the value of the parameters measured corresponds to a maximum admissible load whose value is between the value of two maximum admissible loads stored in the memory, without reducing the reliability of the system, the central unit is able to make an approximation consisting of taking the lower value of the two said maximum admissible loads.
When the diagrams provided by the manufacturer are accurate but on the other hand the capacity of the memories is limited, it is possible to divide each of the curves drawn on the diagrams into sections comprising a simplified mathematical model and to memorise these mathematical models with programming of the central unit such that for each of the values of the pairs of parameters, a central unit calculates the load using the mathematical model assigned to the section corresponding to these parameters. In this case also, when sufficiently complete diagrams are available, it is possible to carry out the afore-mentioned approximation.
When sufficiently complete diagrams are not available, it is possible to calculate the authorized load by incrementation from the values given on the manufacturer's reference diagram whose values have been memorised: